From f736dbeb318386b1292bf00d0199bc3771d849f7 Mon Sep 17 00:00:00 2001
From: "Jason A. Dönerfield" <no-replay@sl0p.foo>
Date: Fri, 17 Jul 2026 00:38:46 +0200
Subject: md2html: let bullet/1. lists interrupt paragraphs (GitHub-style)

Python-Markdown, unlike CommonMark/GitHub, refuses to start a list that
immediately follows a paragraph line without an intervening blank line, so a
very common README shape renders as one run-on paragraph:

    Passing:
    - foo
    - bar

Add a preprocessor that inserts the blank line when a bullet (- * +) or a
1./1) ordered marker follows a paragraph line, restoring GitHub behavior.
Only '1' interrupts for ordered lists (matching CommonMark) so prose like
'... the year\n1985. was ...' is not turned into a list. Fenced/indented
code and lines already inside a list are left untouched.
---
 filters/html-converters/md2html | 55 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/filters/html-converters/md2html b/filters/html-converters/md2html
index de393c7..faa71f3 100755
--- a/filters/html-converters/md2html
+++ b/filters/html-converters/md2html
@@ -2,8 +2,62 @@
 import markdown
 import sys
 import io
+import re
 from pygments.formatters import HtmlFormatter
 from markdown.extensions.toc import TocExtension
+from markdown.extensions import Extension
+from markdown.preprocessors import Preprocessor
+
+# Python-Markdown (unlike CommonMark/GitHub) refuses to let a list interrupt a
+# paragraph unless there's a blank line between them, so a very common README
+# shape renders as one run-on paragraph instead of a list:
+#
+#     Passing:
+#     - foo
+#     - bar
+#
+# This preprocessor restores the GitHub behavior: when a bullet ( - * + ) or a
+# "1."/"1)" ordered-list marker immediately follows a paragraph line, insert a
+# blank line so the list starts. We deliberately only interrupt on "1" for
+# ordered lists (matching CommonMark) so prose like "... the year\n1985. was
+# ..." is not turned into a list. Fenced code, indented code, and lines that
+# already follow a list item are left untouched.
+_MD_FENCE = re.compile(r'^(\s{0,3})(`{3,}|~{3,})')
+_MD_BULLET = re.compile(r'^ {0,3}[-*+][ \t]+\S')
+_MD_ORDERED1 = re.compile(r'^ {0,3}1[.)][ \t]+\S')
+_MD_ANYITEM = re.compile(r'^ {0,3}(?:[-*+]|\d{1,9}[.)])[ \t]')
+
+
+class _ListInterruptPreprocessor(Preprocessor):
+	def run(self, lines):
+		out, in_fence, fence = [], False, None
+		for line in lines:
+			m = _MD_FENCE.match(line)
+			if m:
+				tok = m.group(2)[0]
+				if not in_fence:
+					in_fence, fence = True, tok
+				elif fence == tok:
+					in_fence, fence = False, None
+				out.append(line)
+				continue
+			if not in_fence and out:
+				prev = out[-1]
+				if (prev.strip() and not _MD_ANYITEM.match(prev)
+						and not prev.startswith(('    ', '\t'))
+						and (_MD_BULLET.match(line) or _MD_ORDERED1.match(line))):
+					out.append('')
+			out.append(line)
+		return out
+
+
+class ListInterruptExtension(Extension):
+	def extendMarkdown(self, md):
+		# priority 21: just above the built-in 'normalize_whitespace' (20) so we
+		# operate on clean lines before block parsing.
+		md.preprocessors.register(
+			_ListInterruptPreprocessor(md), 'list_interrupt', 21)
+
 sys.stdin = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8')
 sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-8')
 sys.stdout.write('''
@@ -298,6 +352,7 @@ html = markdown.markdown(
 		"markdown.extensions.codehilite",
 		"markdown.extensions.tables",
 		"markdown.extensions.sane_lists",
+		ListInterruptExtension(),
 		TocExtension(anchorlink=True)],
 	extension_configs={
 		"markdown.extensions.codehilite":{"css_class":"highlight"}})
-- 
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